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Journal of Bacteriology, December 1999, p. 7373-7380, Vol. 181, No. 23
Department of Biology, Biotechnical Faculty,
University of Ljubljana, Ve
Received 26 May 1999/Accepted 23 September 1999
Colicin-producing strains occur frequently in natural populations
of Escherichia coli, and colicinogenicity seems to provide a competitive advantage in the natural habitat. A cka-lacZ
fusion was used to study the regulation of expression of the colicin K
structural gene. Expression is growth phase dependent, with high
activity in the late stationary phase. Nutrient depletion induces the
expression of cka due to an increase in ppGpp. Temperature is a strong signal for cka expression, since only
basal-level activity was detected at 22°C. Mitomycin C induction
demonstrates that cka expression is regulated to a lesser
extent by the SOS response independently of ppGpp. Increased osmolarity
induces a partial increase, while the global regulator integration host factor inhibits expression in the late stationary phase. Induction of
cka was demonstrated to be independent of the cyclic
AMP-Crp complex, carbon source, RpoS, Lrp, H-NS, pH, and short-chain
fatty acids. In contrast to colicin E1, cka expression is
independent of catabolite repression and is partially affected by
anaerobiosis only upon SOS induction. These results indicate that while
different colicins are expressed in response to some common signals
such as nutrient depletion, the expression of individual colicins could be further influenced by specific environmental cues.
Colicins are bacteriocins
synthesized by, and active against, Escherichia coli cells
and sometimes cells of closely related species such as
Shigella and Salmonella. Twenty-three colicin types have been characterized (24). Colicin-producing cells synthesize an immunity protein, which protects the producers against the colicin synthesized inside the same cell or by other cells.
Colicin K kills cells by forming channels in membranes, destroying the
electrochemical potential of the cytoplasmic membrane. Uptake into
sensitive cells requires the outer membrane proteins Tsx, OmpF, TolR,
and TolB. The genes cka, encoding colicin activity, cki, encoding immunity, and ckl, encoding lysis,
have been previously found on pColK-K49 (21) and pColK-K235
(23) of strain BZB2116.
Already studied in detail is the expression of the colicin E1
structural gene. Its regulation has been demonstrated to be complex,
involving repression by LexA, stimulation of transcription by the
cyclic AMP (cAMP) receptor protein (Crp)-cAMP complex (25), Fnr-mediated stimulation of expression in anaerobic conditions (7), and induction by depletion of nutrients (8).
The high frequency of synthesis of colicins in E. coli
strains implies that their role could be the defense or invasion of an
ecological niche. Expression of structural genes of different colicins
could therefore involve common mechanisms of regulation. On the other
hand, strains can produce more than one colicin, and even though
production is induced by some common conditions, e.g., the SOS
response, synthesis of individual colicins could be influenced by
different signals. In the present study, we used a cka-lacZ
fusion to study the regulation of cka expression with regard
to growth phase, nutrient depletion, growth temperature, SOS induction,
and osmotic shock. The role of certain global regulators of gene
expression, i.e., integration host factor (IHF), Lrp, ppGpp, and Crp
(cAMP-Crp), was also investigated.
Our results demonstrate that colicin K synthesis is growth phase
dependent and induced by nutrient depletion due to an increase in
ppGpp. cka expression is strongly influenced by temperature, with only basal-level activity being present at 22°C. The SOS response is not a strong signal for cka expression.
Increased osmolarity partially increases expression, while the global
regulator IHF modulates cka expression negatively with
regard to growth phase. Compared with regulation of expression of the
ColE1 structural gene cea (8), our results
demonstrate that while nutrient depletion induces the synthesis of
ColE1 and colicin K and while LexA is a common repressor, other global
regulatory proteins and environmental conditions modulate synthesis
differently. Such differential regulation could be of ecological
significance, since the synthesis of individual colicins could be
induced by different signals at different sites within the warm-blooded host.
Bacteria and plasmids.
The bacterial strains and plasmids
used in this study are listed in Table 1.
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Transcription Regulation of the Colicin K
cka Gene Reveals Induction of Colicin Synthesis by
Differential Responses to Environmental Signals
gur-Bertok*
na pot 111, 1000 Ljubljana, Slovenia
ABSTRACT
Top
Abstract
Introduction
Materials and Methods
Results
Discussion
References
INTRODUCTION
Top
Abstract
Introduction
Materials and Methods
Results
Discussion
References
MATERIALS AND METHODS
Top
Abstract
Introduction
Materials and Methods
Results
Discussion
References
TABLE 1.
Bacterial strains and plasmids
Media and chemicals.
Strains were grown in Luria-Bertani
(LB) medium with aeration at 37 or at 22°C where indicated. Where
indicated, LB medium was supplemented with 0.3 M NaCl to increase
osmolarity. Ampicillin was used at 100 µg/ml, kanamycin was used at
30 µg/ml, tetracyline was used at 10 µg/ml, and streptomycin was
used at 100 µg/ml. o-Nitrophenyl-
-D-galactopyranoside (ONPG) was
used as substrate in -galactosidase assays of cells treated with
sodium dodecyl sulfate (SDS)-chloroform and washed with Z buffer.
Enzyme activity is defined in units of optical density at 420 nm
(OD420) per minute per unit of OD600
(20).
-galactosidase activity.
cka induction under anaerobic conditions was tested by first
growing bacteria overnight with aeration at 37°C. The bacteria were
grown under the same conditions to 2 × 108 to 4 × 108 cells/ml (OD600 = 1). They were
subsequently diluted 1:100 and grown aerobically for 30 min. The
bacterial culture was then divided into two halves; one was incubated
further aerobically, while the other was incubated in tubes without
aeration for the establishment of anaerobic conditions (7).
However, this is not a strictly anaerobic but a semianaerobic
environment. After 1 h, each culture was split into two parts, and
one was induced with 0.5 µg of mitomycin C per ml.
General DNA manipulation techniques. Plasmid DNA isolation, ligation, and transformation experiments were performed by standard methods (26). Restriction endonuclease digestions were carried out as specified by the supplier (Boehringer). DNA fragments were purified from agarose gels by using the GeneClean II system (Bio 101). DNA-labelling and hybridization experiments were carried out by using the DIG DNA labelling and detection kit (Boehringer). Hybridization experiments were performed to detect the cloned chromosomal colicin K genes by using the 1.15-kb EcoRI-DraI fragment of the cka structural gene. DNA sequencing was performed by a dye rhodamine terminator cycling reaction on an ABI 377 automated sequencer at the Department of Biochemistry, Colorado State University. The relative plasmid pIK471 content was densitometrically determined (13) in all the studied strains and compared at 22 and 37°C.
Cloning of the colicin K genes. Colicin K in strain KS533 (1) is encoded by pColK-JA533. Partially Sau3A1-digested plasmid DNA was cloned into the BamHI site of vector pUC19. A colicinogenic clone was isolated, and the plasmid was designated pIK32. The presence of colicin K-specific genes on plasmid pIK32 was confirmed by DNA hybridization analysis. The location of the cka promoter region with part of the structural gene on an approximately 1-kb EcoRI fragment of plasmid pIK100 was deduced by comparison with the restriction maps of the cka structural, cki immunity, and ckl lysis genes (21). The nucleotide sequence of the cka promoter region was determined by DNA sequencing of the cloned 1-kb EcoRI fragment and is presented in Fig. 1.
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10 region, the Construction of the cka-lacZ gene fusion. PCR was carried out to amplify the 471-bp fragment encompassing 397 nucleotides upstream from the transcription initiation site and 74 nucleotides of the cka structural gene. Two primers were designed, one designated K1 (5'-TCGGATCCATGCGTCTTGCCTGGTATAC-3'pro1) on the basis of the determined promoter region and an added BamHI restriction sequence and the other designated K2 (5'-TCTCTAGATGATTCAGATTCGCCCCTG-3'), corresponding to colicin K nucleotides 74 to 55 (21) and an added XbaI restriction sequence. PCR was carried out in the following steps: heating at 93°C for 5 min followed by 30 cycles of denaturation at 95°C for 1 min, annealing at 61°C for 1 min, and extension at 72°C for 1 min and one final extension for 10 min at 72°C. The PCR-generated fragment was recovered from a 0.9% agarose gel, cut with BamHI and XbaI, and cloned into the promoter probe plasmid pCB267 with the promoterless lacZ gene, also cut with BamHI and XbaI (27), generating pIK471.
Double-stranded nucleotide sequencing with K1 and K2 oligonucleotides as primers was carried out to confirm that no base changes had occurred in cloning the 471-bp amplified fragment in plasmid pIK471.Osmotic pressure.
An overnight culture of the tested strain
was diluted 1:500 into fresh LB medium and grown with aeration at
37°C to mid-exponential phase (OD600 = 0.2). The
culture was then divided into two parts, and to one of these was added
0.3 M NaCl. Samples were periodically removed and assayed for
-galactosidase activity.
Colicin production. Colicin K production was determined by the overlay method (23) by testing the sensitivity of the indicator strain AB1133 (sensitive to all colicins) and immunity of strain BZB2116 with plasmid pColK-K235 (23).
Induction of the SOS response with mitomycin C. Cells of an overnight culture of strain MC4100 with plasmid pIK471 were diluted 1:500 in LB medium and grown with aeration at 37°C. At an OD600 of 0.3, the culture was divided into two parts and to one was added mitomycin C to a concentration of 0.5 µg/ml; the culture was then incubated further.
Temperature-dependent synthesis of colicin K. Cells of an overnight culture of strain MC4100 with plasmid pColK-JA533 were diluted 1:500 in LB medium and grown with aeration at 37°C. At an OD600 of 0.3, the culture was divided into two parts, and to one was added mitomycin C to a concentration of 0.5 µg/ml; the culture was then incubated further for 3 h. Alternatively, to detect Cka at 22°C, an overnight culture of the pColK-JA533-carrying strain was diluted as above and incubated with aeration at 22°C to an OD600 of 2. The culture was subsequently divided into two parts, and to one was added mitomycin C to a concentration of 0.5 µg/ml; the culture was then incubated further for 8 h. A 1.5-ml portion of the cultures was removed, and whole-cell extracts were prepared (24). Samples were analyzed by SDS-polyacrylamide gel electrophoresis.
Nucleotide sequence accession number. The sequence reported in this study has been deposited in the EMBL nucleotide sequence database under accession no. Y18549.
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RESULTS |
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Top
Abstract
Introduction
Materials and Methods
Results
Discussion
References
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cka expression is growth phase dependent.
Overnight cells of strain MC4100 carrying plasmid pIK471 were diluted
1:500 in LB medium and grown with aeration at 37°C (Fig. 2). Dilution of residual
-galactosidase activity from the overnight culture was observed in
the mid-exponential phase, when a basal level of 22 U of
-galactosidase was produced. Expression of -galactosidase activity subsequently increased in a linear manner, with a 17-fold increase in the stationary phase (8 h after inoculation) and a 22-fold
increase, amounting to 490 U, in the late stationary phase.
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Depletion of nutrients induces cka expression. Induction of colicin production in the stationary phase could be due to a variety of changes in the medium, for example, anaerobiosis, pH, depletion of metabolites, excretion of compounds, and high cell density (8). To study the effect of depletion of nutrients, cells were inoculated, at low density (OD600 = 0.015), into medium conditioned for 12 h as described in Materials and Methods. As is evident from Fig. 3, from a basal level a rapid 16-fold increase in activity was established, while growth stopped 3 h after inoculation at an OD600 of 0.062. Subsequently (24 h after inoculation), an approximately 46-fold increase, resulting in 1,026 U, was observed. Activity was thus greater in conditioned medium than in the late-stationary-phase culture which is also depleted of nutrients.
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-galactosidase activity
for up to 3 h after inoculation.
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cka expression is positively affected by ppGpp.
As
cells exhaust nutrients, inbalances occur in amino acid biosynthetic
pathways, resulting in empty acceptor sites in ribosomes and leading to
an increase in guanosine tetraphosphate synthesis. To determine whether
ppGpp is involved in cka expression, the -galactosidase
activity of the cka-lacZ fusion was studied in strain RH98
with mutations in relA and spoT. Strains with
relA spoT double mutations produce no ppGpp. Approximately
eightfold-lower -galactosidase activity was found for the entire
growth cycle in strain RH98 carrying plasmid pIK471 (Fig.
4). These results demonstrate that ppGpp
is a positive effector of cka expression.
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-galactosidase activity of the cka-lacZ
fusion in the relA spoT mutant was approximately 10-fold
lower than that in strain MC4100. cka expression in the relA spoT double mutant was similar in fresh and conditioned
media during the first 8 h. Subsequently, the activity was
approximately twofold higher in conditioned medium, again indicating
that another factor besides ppGpp could be involved in induction of
cka expression.
To rule out the possibility that -galactosidase activity is affected
by changes in the pIK471 copy number, the relative plasmid content was
determined as described in Materials and Methods. In all the studied
strains, the pIK471 copy number was altered only in the relA
spoT mutant. The plasmid content was higher than for strain MC4100
(data not shown). The negative influence of ppGpp on the replication of
a number of plasmids has been previously demonstrated (33).
Our results demonstrate that ppGpp is a positive activator for
induction of cka expression due to depletion of nutrients.
Mitomycin C induces cka expression.
Expression of
colicin activity genes is subject to SOS control with a LexA repressor
binding region located upstream of all colicin activity genes. All ColE
operons and the cka gene have two overlapping SOS boxes in
their regulatory regions (Fig. 1). Induction of cka
expression upon DNA damage was tested in the presence of mitomycin C at
0.5 µg/ml (Table 3). This dose gave the
highest induction with the least killing. Induction with mitomycin C
was observed in the exponential and stationary phases, with approximately threefold and twofold increases in -galactosidase activity, respectively. The relA spoT mutant was also
treated with mitomycin C, and the same level of induction was observed as in the wild-type MC4100 strain (Fig.
5).
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cka expression is repressed by IHF and independent of
S, H-NS, and Lrp.
To determine whether other global
regulator proteins influence cka expression, the
-galactosidase activity of the cka-lacZ fusion was
studied in strains defective in rpoS (RH90), himA
(GE2897), and hns and lrp (GE3653). The results
of our study showed that synthesis and the induction of cka
expression in the stationary phase is H-NS independent (data not
shown). -Galactosidase activity of the cka-lacZ fusion
was even somewhat higher in the rpoS mutant (data not
shown), most probably due to competition between 70 and
S for RNAP core. In the absence of S, the
cellular concentration of the 70-containing holoenzyme
is higher and can result in higher activity of some promoters
(9). Our results show that induction of cka expression is S and Lrp independent. On the other hand
the somewhat higher -galactosidase activity in the late stationary
phase in the himA mutant strain GE2897 indicates that IHF
inhibits cka expression in this phase of the growth cycle
(Table 3).
cka expression is temperature dependent.
To
determine whether the transcription of cka is
thermoregulated, the -galactosidase activity of the
cka-lacZ fusion was monitored when cells were grown at
22°C. cka gene expression is influenced by temperature,
since only 52 U of -galactosidase activity was detected at 22°C
(approximately 10-fold lower than at 37°C). When mitomycin C was
added to the growth medium, fivefold-lower activity at 22°C than at
37°C was observed. Lower activity at 22°C was found not to be due
to lower plasmid copy number (data not shown). These results were
confirmed by SDS-PAGE of the Cka protein, as described in Materials and
Methods (Fig. 6).
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Increased osmolarity affects the expression of cka. Bacterial cells are frequently subjected to fluctuations in the osmolarity of the environment. Osmolarity has been noted to be a signal controlling several virulence genes (19). Under conditions of increased osmolarity, in LB medium supplemented with 0.3 M NaCl, cka-lacZ expression in strain MC4100 was partially increased (Fig. 7).
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Colicin K synthesis is not affected by the cAMP-Crp complex.
To determine whether the cAMP-Crp complex and thus catabolite
repression influences the expression of cka,
-galactosidase activity was monitored in strain SBS688 (defective in
crp, encoding the cAMP receptor protein Crp). cka
expression was shown to be independent of the cAMP-Crp complex (data
not shown).
-Galactosidase activity of strain MC4100 with pIK471 was also tested
in M63 medium supplemented with Casamino Acids and glucose or glycerol
as the carbon source. No differences in -galactosidase activity were
observed, confirming that cka expression is independent of
catabolite repression (data not shown).
Effect of anaerobiosis, pH, and short-chain fatty acids on
cka expression.
The influence of anaerobiosis on
cka expression was monitored under anaerobic (7)
and aerobic conditions in the wild-type MC4100 strain and in the
fnr mutant. We compared the -galactosidase activity of
uninduced cultures and cultures induced with 0.5 µg of mitomycin C
per ml.
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-galactosidase activity of the cka-lacZ
fusion was tested in fresh LB medium adjusted to pH 8.5 with NaOH.
Expression was the same as in LB medium at pH 7 (data not shown),
demonstrating that the increase in pH in the stationary-phase culture
did not affect cka-lacZ expression.
The effects of two short-chain fatty acids, acetic and propionic acids,
on cka-lacZ expression were studied. Sodium salts of both
acids were added at 50 mM to early-log-phase cultures (OD600 = 0.1) of MC4100 carrying pIK471 growing in LB
medium. LB medium supplemented with 50 mM NaCl served as a control.
-Galactosidase activity was determined after 1 h of growth, and
no differences in expression were found between the control medium and
medium containing short-chain fatty acids (data not shown),
demonstrating that accumulation of metabolic products plays no role in
colicin K expression.
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DISCUSSION |
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Top
Abstract
Introduction
Materials and Methods
Results
Discussion
References
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Natural populations of E. coli frequently produce colicins. Recently, the rapid invasion of established colicinogenic populations by another colicinogenic strain expressing novel immunity functions has been demonstrated (29). Studies of regulation of expression of colicin genes and the environmental conditions influencing expression could further elucidate colicin action in the natural environment.
The results presented in this study demonstrate that regulation of colicin K expression is growth phase dependent, with production increasing as cells proceed through the growth cycle. Expression of cka increases in a linear manner as the cells proceed from the exponential to the stationary growth phase. A less pronounced increase in expression is characteristically observed in the late stationary phase. Expression of another pore-forming colicin, colicin E1, has also been shown to be growth phase dependent; however, cea expression is low and constant in the early log phase and then dramatically increases (8).
As cells proceed through the growth cycle, changes in the medium, such as nutrient depletion, pH changes, anaerobiosis, or the production of metabolites or inducers, occur and regulate gene expression. Depletion of nutrients was shown to induce cka expression. Surprisingly, activity in conditioned medium exceeded activity in the stationary phase when the medium was also depleted of nutrients. Complete derepression of cka expression in stationary-phase and late-stationary-phase cultures might be inhibited by cellular remains, which can be used as nutrients for growth.
Bacterial cells of various species sense and respond to population
densities by the production and detection of small signalling substances (pheromones), which regulate a number of processes including
quorum sensing, competence, sporulation, and antibiotic as well as
exoenzyme production (reviewed in references 10, 15,
and 28). Since cka induction in
conditioned medium could be due to the presence of an inducer, the
-galactosidase activity of the cka-lacZ fusion was tested
in conditioned medium complemented by the addition of fresh LB medium.
Expression was initially (in the first 4 h after inoculation)
lower, demonstrating that cka expression is induced in
response to starvation. However, subsequently (after 6 h),
particularly in conditioned medium complemented with 25% fresh LB
medium, expression was significantly greater than in 100% depleted
medium. Our results demonstrated that the addition of low
concentrations of nutrients to conditioned medium induces cka expression to the greatest extent. This effect could be
due to a specific low level of metabolic activity, evidenced as slow growth to an OD600 of 1 to 2. It thus seems that
cka expression is not solely induced by depletion of
nutrients but that another unidentified regulator could also be acting
at a specific physiological state. Since nutrient availability in the
natural bacterial environment is scarce and starvation is common, the
fine-tuning of high levels of cka expression with low
metabolic activity could offer a population of colicin-producing cells
a significant competitive advantage during invasion and establishment
in an ecological niche.
Nutrient depletion in growing bacteria induces the production of guanosine tetraphosphate. ppGpp exerts pleiotropic effects collectively known as the stringent response. Positive stringent control is exerted on processes acting in overcoming amino acid starvation or preparatory for surviving prolonged starvation. ppGpp has been reported to be a positive regulator of rpoS expression (11, 16) and the his operon (5). Our data demonstrate that ppGpp is the main positive effector of cka expression, since only basal-level activity with only an approximately twofold increase in expression occurred in the relA spoT mutant.
The expression of several important virulence determinants is
temperature regulated in a number of bacterial genera (3, 4, 14,
17, 22, 32). By monitoring the -galactosidase activity of the
cka-lacZ fusion at 22 and at 37°C, we demonstrated that
temperature is another important signal influencing cka
expression. At 22°C, only a basal level of -galactosidase activity
was produced in the late stationary phase. Our results thus indicate
that expression of cka is induced in the warm-blooded host.
Repression of colicin synthesis by the LexA protein is a
well-established fact. However, mitomycin C induces only a two- to threefold increase in the -galactosidase activity of
cka-lacZ fusion, indicating that SOS induction is not a
strong regulatory signal for cka expression. Mitomycin C
induction of the cka-lacZ fusion in the relA spoT
mutant, together with induction in the wild-type strain during
exponential growth, demonstrates that ppGpp and the SOS response act
independently in regulating cka expression.
Increased osmolarity induces a partial increase in expression of the cka-lacZ fusion, as determined in medium with 0.3 M NaCl. A partial increase is observed particularly in the stationary phase. As glucose concentrations differ in different parts of the intestinal tract, so do concentrations of salts. Higher concentrations of salts are present in the proximal than in the distal part of the intestinal tract, again indicating that expression of cka could be induced by specific signals in the host.
Our data also demonstrate that in addition to repression by LexA,
cka expression is inhibited in the late stationary phase by
IHF. In the himA mutant strain, cka expression as
determined by -galactosidase activity of the cka-lacZ
fusion is higher in the late stationary phase, when IHF concentrations
increase sixfold. IHF has been proposed to act as an architectural
element and could play an indirect physiological role in gene
expression when other proteins responding to environmental signals
influence IHF binding or activity (2).
Expression of the cka-lacZ fusion is shown to be independent
of the carbon source and the cAMP-Crp complex. It has been reported that virulence factors important for colonization of the proximal part
of the small intestine are expressed independent of the carbon source
and the cAMP-Crp complex, since glucose concentrations are high in this
part of the intestinal tract. On the other hand, the expression of
genes encoding factors crucial in the distal part of the small
intestine is dependent upon the carbon source and the cAMP-Crp complex,
since glucose concentrations are low in this part of the intestinal
tract (reviewed in reference 6). Expression of the
colicin K cka gene is independent of the cAMP-Crp complex
and, in contrast to colicin E1, not significantly affected by
anaerobiosis. On the other hand, the colicin E1 cea gene is dependent on both conditions (7, 25). This implies that
different colicins, even though responding to some common signals, also respond to specific cues. A comparison of the factors affecting the
expression of the colicin K cka gene and the E1
cea gene (7, 8) is presented in Table
5. With regard to nutrient availability and colicin production, lower levels of colicin E3, E5, E6, E8, and E9
production in minimal media than in LB medium have been reported
(29), further demonstrating the differential expression of
various colicins.
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Our results, together with results from other groups, demonstrate that regulation of colicin synthesis is complex and that environmental signals in the host could play an important role in regulation of expression. Two SOS boxes are present in the promoter region of colicin K (Fig. 1) and of ColE operons. It has been proposed that LexA binding to the two overlapping SOS boxes protects colicin-producing cells from lysis under conditions that do not induce the SOS response, since lysis is lethal to the producing cell (18). Growth phase-dependent colicin induction has been reported to be independent of LexA cleavage (8). Intracellular LexA concentrations vary following DNA damage and not with regard to growth phase and environmental cues, like the concentrations of other regulators. Thus, LexA represses colicin expression, preventing cell lysis, until specific environmental signals, e.g., nutrient depletion, temperature, and osmolarity, induce colicin synthesis in the host. The differential induction of at least some colicins by specific environmental signals suggests that individual colicins could be acting and imposing a competitive advantage at different sites within the natural environment. Colicinogenic strains producing more than one colicin could have a competitive advantage under several different environmental conditions.
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ACKNOWLEDGMENTS |
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This work was supported by a grant from the Slovene Ministry of Science and Technology to Irena Kuhar.
We thank J. Blazquez, R. Hengge-Aronis, A. P. Pugsley, H. Yamada, and G. M. Weinstock for providing bacterial strains.
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FOOTNOTES |
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*
Corresponding author. Mailing address: Department of
Biology, Biotechnical Faculty, University of Ljubljana, Vena pot
111, 1000 Ljubljana, Slovenia. Phone: 386 61 123 33 88. Fax: 386 61 273 390. E-mail: Darja.Zgur{at}uni-Lj.Si.
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REFERENCES |
|---|
|
Top
Abstract
Introduction
Materials and Methods
Results
Discussion
References
|
|---|
| 1. |
Ambro i, J.,
A. Ostrover nik,
M. Stari,
I. Kuhar,
M. Grabnar, and D. gur-Bertok.
1998.
Escherichia coli ColV plasmid pRK100: genetic organization, stability and conjugal transfer.
Microbiology
144:343-352 |
| 2. | Aviv, M., H. Giladi, G. Schreider, A. B. Oppenheim, and G. Glaser. 1994. Expression of the genes coding for the Escherichia coli integration host factor are controlled by growth phase, rpoS, ppGpp and by autoregulation. Mol. Microbiol. 14:1021-1031[Medline]. |
| 3. |
Coote, J. G.
1991.
Antigenic switching and pathogenicity: environmental effects on virulence gene expression in Bordetella pertussis.
J. Gen. Microbiol.
137:2493-2503 |
| 4. | Cornelis, G. R., T. Biot, C. Lambert de Rouvroit, T. Michelies, B. Mulder, C. Sluiters, et al. 1989. The Yersinia yop regulon. Mol. Microbiol. 3:1455-1459[Medline]. |
| 5. |
Da Costa, X. J., and S. W. Artz.
1997.
Mutations that render the promoter of the histidine operon of Salmonella typhimurium insensitive to nutrient-rich medium repression and amino acid downshift.
J. Bacteriol.
179:5211-5217 |
| 6. | Edwards, R. A., and J. L. Puente. 1998. Fimbrial expression in enteric bacteria: a critical step in intestinal pathogenesis. Trends Microbiol. 6:282-287[Medline]. |
| 7. |
Eraso, J. M., and G. M. Weinstock.
1992.
Anaerobic control of colicin E1 production.
J. Bacteriol.
174:5101-5109 |
| 8. |
Eraso, J. M.,
M. Chidambaram, and G. M. Weinstock.
1996.
Increased production of colicin E1 in stationary phase.
J. Bacteriol.
178:1928-1935 |
| 9. | Farewell, A., K. Kvint, and T. Nystrom. 1998. Negative regulation by RpoS: a case of sigma factor competition. Mol. Microbiol. 29:1039-1051[Medline]. |
| 10. | Fuqua, C., S. C. Winans, and E. P. Greenberg. 1996. Census and consensus in bacterial ecosystems: the LuxR-LuxI family of quorum sensing transcriptional regulators. Annu. Rev. Microbiol. 50:727-751[Medline]. |
| 11. |
Gentry, D. R.,
V. J. Hernandez,
L. H. Nguyen,
D. B. Jensen, and M. Cashel.
1993.
Synthesis of stationary-phase S is positively regulated by ppGpp.
J. Bacteriol.
175:7982-7989 |
| 12. |
Gomez-Gomez, J. M.,
F. Baquero, and J. Blazquez.
1996.
Cyclic AMP receptor protein positively controls gyrA transcription and alters DNA topology after nutritional upshift in Escherichia coli.
J. Bacteriol.
178:3331-3334 |
| 13. | Hiszcynska-Sawicka, E., and J. Kur. 1997. Effect of Escherichia coli IHF mutations on plasmid p15A copy number. Plasmid 38:174-179[Medline]. |
| 14. | Jordi, B. J. A. M., B. Dagberg, L. A. M. deHaan, A. M. Hamers, B. A. M. van de Zeijst, and W. Gaastra. 1992. The positive regulator cfaD overcomes the repression mediated by the histone-like protein H-NS (H1) in the CFA/I fimbrial operon of Escherichia coli. EMBO J. 11:2627-2632[Medline]. |
| 15. | Kleerebezem, M., L. E. N. Quadri, O. P. Kuipers, and W. M. de Vos. 1997. Quorum sensing by peptide pheromones and two-component signal transduction systems in Gram-positive bacteria. Mol. Microbiol. 24:895-904[Medline]. |
| 16. |
Lange, R.,
D. Fischer, and R. Hengge-Aronis.
1995.
Identification of transcriptional start sites and the role of ppGpp in the expression of rpoS, the structural gene for the S subunit of RNA polymerase in Escherichia coli.
J. Bacteriol.
177:4676-4680 |
| 17. |
Leimester, M.,
E. Domann, and T. Chakraborty.
1992.
The expression of virulence genes in Listeria monocytogenes is thermoregulated.
J. Bacteriol.
174:947-952 |
| 18. | Lu, F.-M., and K.-F. Chak. 1996. Two overlapping SOS-boxes in ColE operons are responsible for the viability of cells harboring the Col plasmid. Mol. Gen. Genet. 251:407-411[Medline]. |
| 19. |
Mekalanos, J. J.
1992.
Environmental signals controlling expression of virulence determinants in bacteria.
J. Bacteriol.
174:1-7 |
| 20. | Miller, J. H. 1972. Experiments in molecular genetics. Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y |
| 21. |
Pilsl, H., and V. Braun.
1995.
Strong function-related homology between the pore-forming colicins K and 5.
J. Bacteriol.
177:6973-6977 |
| 22. | Puente, J. L., D. Bieber, S. W. Ramer, W. Murray, and G. K. Schoolnik. 1996. The bundle-forming pili of enteropathogenic Escherichia coli: transcriptional regulation by environmental signals. Mol. Microbiol. 20:87-100[Medline]. |
| 23. |
Pugsley, A. P.
1985.
Escherichia coli K12 strains for use in the identification and characterisation of colicins.
J. Gen. Microbiol
131:369-376 |
| 24. | Pugsley, A. P., and B. Oudega. 1987. Methods for studying colicins and their plasmids, p. 105-161. In K. G. Hardy (ed.), Plasmids, a practical approach. IRL Press, Oxford, United Kingdom |
| 25. | Salles, B., and G. M. Weinstock. 1989. Interaction of the CRP-cAMP complex with the cea regulatory region. Mol. Gen. Genet. 215:537-542[Medline]. |
| 26. | Sambrook, J., E. F. Fritsch, and T. Maniatis. 1989. Molecular cloning: a laboratory manual, 2nd ed. Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y |
| 27. | Schneider, K., and C. F. Beck. 1986. Promoter-probe vectors for the analysis of divergently arranged promoters. Gene 42:37-48[Medline]. |
| 28. | Sitnikov, D. M., J. B. Schineller, and T. O. Baldwin. 1995. Transcriptional regulation of bioluminescence genes from Vibrio fischeri. Mol. Microbiol. 17:801-812[Medline]. |
| 29. |
Tan, Y., and M. A. Riley.
1996.
Rapid invasion of colicinogenic Escherichia coli with novel immunity functions.
Microbiology
142:2175-2180 |
| 30. | Yamamada, H., T. Yoshida, K. Tanaka, C. Sasakawa, and T. Mizuno. 1991. Molecular analysis of the E. coli hns gene encoding a DNA-binding protein, which preferentially recognizes curved DNA sequences. Mol. Gen. Genet. 230:332-336[Medline]. |
| 31. | Yanisch-Perron, C., J. Vieira, and J. Messing. 1985. Improved M13 phage cloning vectors and host strains: nucleotide sequences of the M13mp18 and pUC19 vectors. Gene 33:103-109[Medline]. |
| 32. |
White-Zeigler, C. A.,
L. B. Blyn,
B. A. Braaten, and D. A. Low.
1990.
Identification of a genetic locus in Escherichia coli involved in the thermoregulation of the pap operon.
J. Bacteriol.
172:1775-1782 |
| 33. | Wrobel, B., and G. Wegrzyn. 1997. Replication of plasmids derived from P1, F, R1, R6K, RK2 replicons in amino acid-starved Escherichia coli stringent and relaxed strains. J. Basic Microbiol. 37:451-463[Medline]. |
Journal of Bacteriology, December 1999, p. 7373-7380, Vol. 181, No. 23
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